This book stems from an earlier publication, "Natural Toxins. The Good, The Bad and The Deadly". (Wright 2025) dealing with the bioactive properties of organisms including their interactions with each other and with their natural environment. The current work reects a resurgence of interest in fungi, a group of organisms that have only recently been recognised as unique life-forms with no direct taxonomic relationship with existing phyla such as plants, animals or bacteria. The cryptic lifestyle of fungi, often in close physical association with other phyla, has resulted in both beneficial and harmful effects on host organisms and on consumers including humans. These properties have also contributed to a rich folklore that has accompanied fungi throughout their history.